GB907464A - Process for the preparation of cyanuric acid from urea or biuret - Google Patents

Abstract

A reaction mixture containing cyanuric acid is prepared by heating a mixture of a methylcyclohexyl carbamate with urea or biuret. The initial charge of the methylcyclohexyl carbamate may be prepared by refluxing the corresponding alcohol at 165 DEG -175 DEG C. and adding urea or biuret, which reacts with the alcohol to form the carbamate, with a resulting rise in refluxing temperature. Further addition of urea or biuret results in the formation of cyanuric acid, which may be separated from the reaction mixture, e.g. by filtration, and the carbmate is returned to the reactor and the steps repeated. In continuous operation, urea or biuret is continuously added to the reaction mixture while a portion of the latter is continuously removed, filtered, and returned to the reactor. The preferred reaction temperature is in the range 200 DEG -215 DEG C., and specified carbamates are those of 2-, 3- and 4-methylcyclohexanol and mixtures of any of them. Example I illustrates the use of 3-methylcyclohexyl carbamate, while Examples II to IV illustrate the use of a mixture of 3- and 4-methylcyclohexyl carbamates, of 4-methylcyclohexyl carbamate, and 2-methylcyclohexyl carbamate respectively. The yields are 90% and above, of pure cyanuric acid. Cyanuric acid in the product, which may also contain small amounts of urea, biuret, and amonelide, may be individually quantitatively estimated by precipitating a copper-cyanuric acid complex, separating and redissolving the complex in sulphuric acid, liberating the copper from the complex with potassium iodide, and finally titrating the resulting iodine with standard thiosulphate in the presence of starch. This analysis is stated to be specific for cyanuric acid in the presence of the above mentioned impurities. U.S.A. Specifications 2,822,363 and 2,872,447 are referred to.